From 7f318327e57122c7f49bdef9915153f6956a5c7d Mon Sep 17 00:00:00 2001
From: Sona Kurazyan <sona.kurazyan@qt.io>
Date: Thu, 20 Jan 2022 14:02:34 +0100
Subject: [PATCH] QtConcurrent: use variable templates for compile-time checks

Noticed during the API review.

Pick-to: 6.3 6.2
Task-number: QTBUG-99883
Change-Id: I19571343a0cf0609beae2422ef1f69f7a34eb9ac
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/concurrent/qtconcurrentfilter.h           |  4 ++--
 src/concurrent/qtconcurrentfunctionwrappers.h | 19 ++++++-------------
 src/concurrent/qtconcurrentmap.h              |  4 ++--
 3 files changed, 10 insertions(+), 17 deletions(-)

diff --git a/src/concurrent/qtconcurrentfilter.h b/src/concurrent/qtconcurrentfilter.h
index dce4f35db6..2fdc8f9d0f 100644
--- a/src/concurrent/qtconcurrentfilter.h
+++ b/src/concurrent/qtconcurrentfilter.h
@@ -333,7 +333,7 @@ QFuture<ResultType> filteredReduced(QThreadPool *pool,
 }
 
 template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
-          std::enable_if_t<QtPrivate::isIterator<Iterator>::value, int> = 0,
+          std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
           std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
@@ -673,7 +673,7 @@ ResultType blockingFilteredReduced(QThreadPool *pool,
 }
 
 template <typename Iterator, typename KeepFunctor, typename ReduceFunctor,
-          std::enable_if_t<QtPrivate::isIterator<Iterator>::value, int> = 0,
+          std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
           std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
diff --git a/src/concurrent/qtconcurrentfunctionwrappers.h b/src/concurrent/qtconcurrentfunctionwrappers.h
index 08966115d6..e9154070bc 100644
--- a/src/concurrent/qtconcurrentfunctionwrappers.h
+++ b/src/concurrent/qtconcurrentfunctionwrappers.h
@@ -142,24 +142,17 @@ struct ReduceResultType<T(C::*)(U) noexcept>
 };
 
 template<class T, class Enable = void>
-struct hasCallOperator : std::false_type
-{
-};
+inline constexpr bool hasCallOperator_v = false;
 
 template<class T>
-struct hasCallOperator<T, std::void_t<decltype(&T::operator())>> : std::true_type
-{
-};
+inline constexpr bool hasCallOperator_v<T, std::void_t<decltype(&T::operator())>> = true;
 
 template<class T, class Enable = void>
-struct isIterator : std::false_type
-{
-};
+inline constexpr bool isIterator_v = false;
 
 template<class T>
-struct isIterator<T, std::void_t<typename std::iterator_traits<T>::value_type>> : std::true_type
-{
-};
+inline constexpr bool isIterator_v<T, std::void_t<typename std::iterator_traits<T>::value_type>> =
+        true;
 
 template <class Callable, class Sequence>
 using isInvocable = std::is_invocable<Callable, typename std::decay_t<Sequence>::value_type>;
@@ -180,7 +173,7 @@ struct ReduceResultTypeHelper<Callable,
 template <class Callable>
 struct ReduceResultTypeHelper<Callable,
         typename std::enable_if_t<!std::is_function_v<std::remove_pointer_t<std::decay_t<Callable>>>
-                                  && hasCallOperator<std::decay_t<Callable>>::value>>
+                                  && hasCallOperator_v<std::decay_t<Callable>>>>
 {
     using type = std::decay_t<typename QtPrivate::ArgResolver<Callable>::First>;
 };
diff --git a/src/concurrent/qtconcurrentmap.h b/src/concurrent/qtconcurrentmap.h
index 3e20f8b4dc..64e9fe938c 100644
--- a/src/concurrent/qtconcurrentmap.h
+++ b/src/concurrent/qtconcurrentmap.h
@@ -352,7 +352,7 @@ template <typename Iterator, typename MapFunctor, typename ReduceFunctor, typena
           typename InitialValueType>
 #else
 template<typename Iterator, typename MapFunctor, typename ReduceFunctor,
-         std::enable_if_t<QtPrivate::isIterator<Iterator>::value, int> = 0,
+         std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
          typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
          typename InitialValueType,
          std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>
@@ -739,7 +739,7 @@ template <typename Iterator, typename MapFunctor, typename ReduceFunctor, typena
           typename InitialValueType>
 #else
 template <typename Iterator, typename MapFunctor, typename ReduceFunctor,
-          std::enable_if_t<QtPrivate::isIterator<Iterator>::value, int> = 0,
+          std::enable_if_t<QtPrivate::isIterator_v<Iterator>, int> = 0,
           typename ResultType = typename QtPrivate::ReduceResultTypeHelper<ReduceFunctor>::type,
           typename InitialValueType,
           std::enable_if_t<std::is_convertible_v<InitialValueType, ResultType>, int> = 0>